The present invention relates to an antenna structure for a wireless communication device.
Nowadays, many vehicles are equipped with a hands-free system to improve vehicle operation convenience. For example, a hands-free system locks and unlocks vehicle doors, enables the engine to be started, and actually starts the engine. Such type of a hands-free system includes a low frequency (LF) transmitter and a radio frequency (RF) receiver, which are arranged in a vehicle. The hands-free system communicates with a portable device, which is carried by a user (driver) and functions as a key. The LF transmitter intermittently transmits a request signal in a low frequency band. In response to the request signal, the portable device returns an ID code signal in a radio frequency band. The ID code signal includes an identification (ID) code that is unique to the portable device, or key. The RF receiver receives the ID code signal. Then, the ID code of the portable device is compared with an ID code of the vehicle. When the ID codes match, the portable device is verified as being authentic. In such a case, the vehicle doors can be locked or unlocked, the starting of the engine is enabled, and the engine may actually be started.
Such type of a portable device incorporates a receiving antenna, which receives the request signal transmitted from the vehicle, and a transmitting antenna, which transmits to the vehicle the ID code signal that is unique to the key, in order to perform wireless communication. One example of an antenna used in a portable device is a pattern antenna. The pattern antenna is formed by printing the pattern of an antenna onto a substrate that supports wireless communication components of the portable device (refer to, for example, Japanese Laid-Open Patent Publication No. 7-113365). The use of a pattern antenna, which is printed on a substrate, eliminates the need for separate antenna components that are independent from the substrate. Thus, the portable device may be formed with fewer components.
The human body may block radio waves when the portable device is performing wireless communication. The portable device is often carried by a user in a clothing pocket. In such a state, the portable device would be in substantial contact with the human body. Thus, the human body may interfere with the portable device and lower the intensity of transmitted radio waves. Thus, even if the pattern antenna of the portable device attempts to transmit a signal to the vehicle, the transmitted radio wave may not reach the vehicle in a normal manner due to the lowered intensity of the transmitted radio waves. In such a case, the portable device would not be able to communicate radio waves with the vehicle in a normal manner. Thus, the portable device would not function normally and the user would not be able to perform the desired vehicle operation even though the user is carrying the portable device. Such a situation would be annoying to the user. The same problem may occur when the user performs a vehicle operation while gripping the portable device such that the pattern antenna is blocked by the user's hand.